# Fail2ban

> Fail2Ban

- Skill: `comeonoliver/fail2ban` (Agent Skill)
- Install (CLI): `npx skillmds@latest add comeonoliver/fail2ban`
- Raw SKILL.md: https://api.skillmd.com/api/skills/comeonoliver/fail2ban/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ComeOnOliver (https://skillmd.com/u/comeonoliver)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/comeonoliver/fail2ban

---

# Fail2Ban

## Overview

Fail2Ban monitors log files for failed authentication attempts and bans offending IPs using iptables/nftables. Protects SSH, Nginx, Apache, Postfix, and any service with log-based authentication.

## Instructions

### Step 1: Install

```bash
sudo apt install fail2ban
sudo systemctl enable fail2ban
```

### Step 2: Configure

```ini
# /etc/fail2ban/jail.local — Custom configuration (never edit jail.conf)
[DEFAULT]
bantime = 1h
findtime = 10m
maxretry = 5
banaction = iptables-multiport

[sshd]
enabled = true
port = ssh
maxretry = 3
bantime = 24h

[nginx-http-auth]
enabled = true
port = http,https
maxretry = 5

[nginx-botsearch]
enabled = true
port = http,https
maxretry = 2
bantime = 7d
```

### Step 3: Monitor

```bash
sudo fail2ban-client status               # list active jails
sudo fail2ban-client status sshd           # show banned IPs
sudo fail2ban-client set sshd unbanip 1.2.3.4   # unban
sudo fail2ban-client set sshd banip 5.6.7.8     # manual ban
```

## Guidelines

- Always create jail.local — jail.conf gets overwritten on updates.
- Start conservative: 5 retries, 1h ban. Adjust based on logs.
- For modern alternative with community threat sharing, consider CrowdSec.
- Use `fail2ban-regex` to test custom filters before deploying.